Magnetic encoder

ABSTRACT

A magnetic encoder having a magnetic sensor composed of SVGMR elements, in which a signal output with a cycle equal to or less than a third of a cycle of magnetic patterns on a magnetic medium. The magnetic encoder comprises the magnetic medium, on which first magnetic regions and second magnetic regions are oppositely magnetized along the medium extending and disposed successively and alternately with each other, and the sensor that has three SVGMR elements or more and is movable relatively to the medium along the medium extending. Magnetizations of pinned magnetization layers of all the SVGMR elements are directed in the same direction along the medium extending. The SVGMR elements in the sensor are apart from each other along the medium extending by a length p, defined by 1/(the number N of the SVGMR elements in the sensor) of the sum of a first magnetic region length plus a second magnetic region length, and the SVGMR elements in the sensor are connected in series so that a cycle of resistance change of the sensor is 1/N of a cycle length of magnetic patterns on the medium, and the signal output with high resolution can be obtained.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic encoder using a magneticsensor with a spin-valve type giant magneto-resistance effect film.

2. Description of the Related Art

In recent years, a magnetic encoder applied to civil appliances, such assmall-sized robots, digital cameras and ink-jet printers, is requirednot only to be cheap and small-sized but also to have the highresolution and excellent gap output characteristics. In other words, itis required that a magnetic encoder is small-sized but does not need aprocessing circuit for doubling frequency of signal and also canmaintain a stable output against gap variation during its operation.Further, low electric power consumption is required.

In a conventional magnetic encoder, magnetic resistors formed from ananisotropic magneto-resistance effect film (hereinafter referred to as“AMR element”) are applied. The AMR elements are widely used, becauseelectric resistance is changed by some percent by a magnetic fieldchange in them even in a region of a relatively small magnetic field,and because their films are easily produced. However, it is necessary tothicken the film to 20 nm to 40 nm, in order to obtain a stablemagneto-resistance effect for the AMR elements having NiFe alloy thinfirm or NiCo alloy thin film. But, they are difficult to use, sinceelectric resistance of the elements reduces due to the thicker film. Ifa width dimension of the AMR element is reduced to increase theresolution, a shape anisotropy (Hk) is increased together with aninfluence of the thicker film, and a sufficient electric resistancechange cannot be obtained in a region of a weak magnetic field to causean expected electric output. Because of the reason, it was difficult toenhance the resolution in a magnetic encoder using AMR elements.Increase of the resolution means narrowing pitches of the elementsand/or magnetizations on a medium and also increase of the number of theelectric output signals for a unit length.

Instead of the AMR elements, which are difficult to enhance resolution,an element using a coupled giant magneto-resistance effect film(hereinafter referred to as “coupled GMR elements”) is disclosed inJapanese Patent 2812042. The coupled GMR element has an electricresistance variation ratio as much as twice to four times of the AMRelement. In the coupled GMR elements described in Japanese Patent2812042, an artificial lattice metallic film having some-ten layers ofalternately laminated NiCoFe thin films and non-magnetic metal thinfilms is used. The multiple lamination of the ferro-magnetic thin filmsand the non-magnetic metal thin films leads to a largemagneto-resistance variation ratio. However, it is difficult toaccomplish a low electric power consumption, since the non-magneticmetal thin films are a good electrically conductive material and theelectric resistance of the film is as low as a half to a third of thatof an AMR element. The coupled GMR elements have an electric resistancevariation ratio as much as 20% to 30%, but the electric resistancevariation ratio can be obtained only by using them in a large magneticfield. By the reason, it was hard to use them in a relatively smallmagnetic field as in a magnetic encoder.

There is a spin-valve type giant magneto-resistance effect film as usedin a magnetic head of a hard disk storage device (HDD), which is a filmshowing, in a region of a relatively small magnetic field, an electricresistance variation ratio as much as a coupled GMR element. Asdescribed in Japanese Patent 3040750, the spin-valve type giantmagneto-resistance effect film is composed of a pinned magnetizationlayer, in which a magnetization direction is not changed by a variationon an external magnetic field (or magnetic flux) direction, anon-magnetic conductive layer and a free magnetization layer, in which amagnetization direction is changed following a variation of an externalmagnetic field. An element made from a spin-valve type giantmagneto-resistance effect film (hereinafter referred to as “SVGMRelement”) has an electric resistance as large as five times to six timesof that of the coupled GoM element, and reduction of electric powerconsumption is easily achieved when it is used for a magnetic sensor.Also, it can work in a region of a magnetic field as relatively small as1 A/m to 160 A/m, that is, about 0.006 Oe to 20 Oe.

However, a magnetic encoder has a disadvantage that resolution isreduced by only a substitution of the SVGMR elements for AMR elementsand coupled GMR elements. When the SVGMR elements are used with amagnetic medium alternately magnetized with N-poles and S-poles with amagnetized pitch λ, a signal has an output cycle of 2λ that is twice ofthe magnetized pitch. In other words, the resolution becomes a half.This is caused by a magneto-resistance variation characteristic, and thereduction in the resolution cannot be avoided in a conventional encoderstructure.

This is because the SVGMR elements have characteristic that electricresistance of the elements changes when an external magnetic field isapplied in the same direction as magnetizations of pinned magnetizationlayers in the elements, while it does not change when the externalmagnetic field is applied oppositely. Or, because the SVGMR elementshave characteristic that electric resistance of the elements does notchange when an external magnetic field is applied in the same directionas magnetizations of pinned magnetization layers in the elements, whileit changes when the external magnetic field is applied oppositely. Whena magnetic medium is magnetized with a magnetized pitch λ, a magneticfield direction changes for every λ. Because of that, electricresistance of SVGMR elements changes with a cycle of 2λ that is twice ofthe magnetized pitch. By contrast, using coupled GMR elements or AMRelements provides an electric signal of a cycle of λ. The coupled G(MRelements and AMR elements show maximum electric resistances in a stateof no magnetic field, and the electric resistances reduce when anexternal magnetic field increases. That is, regardless of a magneticfield direction, a signal is caused by increase and decrease of magneticfield intensity. From the reason, an electric signal of the same cycleas the magnetized pitch λ can be obtained. SVGMR elements have not beenapplied to a magnetic encoder because they hardly satisfy the highresolution that is demanded in a market. However, since the SVGMRelements show a magneto-resistance variation ratio as much as in coupledGMR elements in a region of a relatively small magnetic field and alsoan electric resistance as large as five times to six times that of thecoupled GMR elements, it is hard to give up an advantage that a lowelectric power consumption can be easily accomplished by the SVGMRelements.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a magnetic encoder,which comprises a magnetic sensor composed of SVGVR elements and amagnetic medium that has successively magnetizations alternatelymagnetized in opposite directions, that provides an electric signalhaving a cycle equal to or less than a third of a magnetized patterncycle of the magnetic medium, a low electric power consumption in themagnetic encoder and a stable output property with respect to a gapvariation.

A magnetic encoder according to the present invention comprises: amagnetic medium extending in a direction and having first magnetizedregions and second magnetized regions, which are disposed successivelyand alternately with each other on the medium and magnetized oppositelyto one another along the medium, and a magnetic sensor movablerelatively to the medium along the medium extending. The firstmagnetized regions and the second magnetized regions have differentlength from one another, and a length of longer ones of them is denotedas λl and a length of shorter ones of them is denoted as λs. Themagnetic sensor is composed of a first sensor and a second sensor. Eachof the first and the second sensors is composed of SVGMR elements of theequal number N of three or more, which have a rectangular flat surfaceextending perpendicularly to the medium extending and are electricallyconnected in series. Each of the SVGMR elements in each of the first andthe second sensors is apart by a length p defined by (λl+λs)/N fromanother SVGMR element along the medium extending. One of the SVGMRelements of the first sensor is at a distance of p(½+n) along the mediumextending from an SVGMR element in the second sensor, in which n is zeroor a positive integer. Each of the SVGMR elements is a lamination of apinned magnetization layer, a non-magnetic conductive layer and a freemagnetization layer in their order, and the pinned magnetization layersin all the SVGMR elements have magnetizations in the same directionalong the medium extending. The SVGMR elements show a minimum electricresistance, when an external magnetic field is applied to the SVGMRelements in the same direction as the magnetizations of the pinnedmagnetization layers of the SVGMR elements, and a maximum electricresistance, when an external magnetic field is applied to the SVGMRelements in the direction opposite to the magnetizations of the pinnedmagnetization layers of the SVGMR elements.

An electric terminal of the first sensor, that is, one of open electricterminals of the SVGMR elements forming the first sensor, iselectrically connected to an electric terminal of the second sensor,that is, one of open electric terminals of the SVGMR elements formingthe second sensor. A measurement voltage is applied between the otherelectric terminal of the first sensor, that is, the other of the openelectric terminals of the SVGMR elements forming the first sensor, andthe other electric terminal of the second sensor, that is, the other ofthe open electric terminals of the SVGMR elements forming the secondsensor. A signal output is taken out from the connected electricterminals between the first sensor and the second sensor.

An SVGMR element shows a maximum resistance against an electric currentflowing through the SVGMR element, when a magnetization of a freemagnetization layer is anti-parallel to a magnetization of a pinnedmagnetization layer in the SVGMR element, while the SVGMR element showsa minimum resistance, when the magnetization of the free magnetizationlayer is parallel to the magnetization of the pinned magnetization layerin the SVGMR element. In an SVGMR element applicable to the presentinvention, a magnetization of a free magnetization layer isanti-parallel to a magnetization of a pinned magnetization layer in thestate that an external magnetic field is not applied to the SVGMRelement or is applied in the direction opposite to the magnetization ofthe pinned magnetization layer, and when the external magnetic field isapplied in the same direction as the magnetization of the pinnedmagnetization layer, the magnetization of the free magnetization layerturns in the same direction as the external magnetic field, that is, asthe magnetization of the pinned magnetization layer, and when theexternal magnetic field is increased to a sufficient strength, themagnetization of the free magnetization layer becomes parallel to themagnetization of the pinned magnetization layer, and the SVGMR elementshows a minimum resistance. Alternatively, when an external magneticfield is not applied to an SVGMR element or is applied in the samedirection as a magnetization of a pinned magnetization layer, amagnetization of a free magnetization layer is parallel to themagnetization of the pinned magnetization layer, and the SVGMR elementshows a minimum resistance, and when the external magnetic field isapplied in the direction opposite to the magnetization of the pinnedmagnetization layer, the magnetization of the free magnetization layerturns in the same direction as the external magnetic field, that is, inthe direction opposite to the magnetization of the pinned magnetizationlayer, and then, when the external magnetic field becomes to asufficient strength, the magnetization of the free magnetization layeris anti-parallel to the magnetization of the pinned magnetization layer,and the SVGMR element shows a maximum resistance.

In an SVGMR element, it is determined by materials of a pinnedmagnetization layer and/or a free magnetization layer and thickness of anon-magnetic conductive layer interposed between the pinnedmagnetization layer and the free magnetization layer whether amagnetization of the free magnetization layer is parallel oranti-parallel to a magnetization of the pinned magnetization layer inthe state of no external magnetic field applied.

The magnetic encoder of the present invention may use a magnetic mediumthat is formed on a periphery or an end surface of a round disk orformed in a linear magnetic scale. Since a shape of a magnetic mediumfor a magnetic encoder is widely known, a detailed description isomitted here.

In the magnetic medium for the magnetic encoder of the presentinvention, it is necessary that the first magnetized region is differentin length from the second magnetized region. When a high portion (amountain) is formed in resistance by a longer region of the first andthe second magnetized regions, overlap of the high portion of resistancewith a neighboring high portion of resistance appears, and a differencein resistance between the overlapped high portion and a non-overlappedhigh portion develops. When a high portion (a mountain) is formed inresistance by a shorter region of the first and the second magnetizedregions, a skirt of a high portion in resistance does not overlap askirt of a neighboring high portion in resistance, so that a differencein resistance between a high portion and a low portion develops. But,when the first magnetized region has a length equal to the secondmagnetized region, a skirt of a high portion in resistance overlaps askirt of a neighboring high portion in resistance so that a low portionin resistance does not appear, and a difference in resistance is reducedso that it is difficult to take out an output.

In the magnetic encoder of the present invention, each of the first andthe second sensors is composed of N pieces of SVGMR elements, each ofwhich is apart by p from another along the medium extending. When anSVGMR element is located to face a first magnetized region or a secondmagnetized region, a resistance of the SVGMR element changes from aminimum value R2 to a maximum value R1 to show a mountain of resistance.Since each of the sensors is composed of the N pieces of SVGMR elementsthat are connected in series and apart by p from another, a resistancemountain is caused with an interval p by the SVGMR elements, and asignal output from each of the first and the second sensors has a cycleof 1/N of a magnetic pattern cycle (λl+λs) of the magnetic medium.

Since the first sensor and the second sensor are apart by a distancep(½+n), expressed by a length p defined by (λl+λs)/N and a positiveinteger n including zero, from each other along the medium extending inthe magnetic encoder of the present invention, a resistance pattern ofthe first sensor is different by ½·p in phase from that of the secondsensor. Taking out a midpoint electric potential between the firstsensor and the second sensor as a signal output, a bridge output can beobtained.

Furthermore, in the magnetic encoder of the present invention, it ispreferable that a width w of each of the SVGMR elements along the mediumextending is equal to or less than λs.

A portion of a resistance changing has a length w in a resistancemountain of an SVGMR element that repeats with an interval p. Presumingthat an SVGMR element shows a maximum resistance R1, when it ispositioned to face a first magnetized region, and a minimum resistanceR2, when it is positioned to face a second magnetized region, the SVGMRelement has a resistance R2, since the SVGMR element faces the secondmagnetized region when it is w before a front edge of the firstmagnetized region. When it further approaches the first magnetizedregion from a location that is w before the front edge of the firstmagnetized region, a part of the SVGMR element comes to face the firstmagnetized region, and a magnetization of a free magnetization layer theSVGMR element begins to turn by an influence of the first magnetizedregion from a position where the magnetization of the free magnetizationlayer is parallel to that of the pinned magnetization layer. So, theresistance of the SVGMR element rises from the minimum value R2. Whenthe extent of the SVGMR element facing the first magnetized regionfurther increases, the resistance increases, and the magnetization ofthe free magnetization layer of the SVGMR element becomes anti-parallelto the magnetization of the pinned magnetization layer to make theresistance almost the maximum value R1, when the SVGMR element reaches alocation where it completely faces the first magnetized region. TheSVGMR element proceeds from the location w here it faces the firstmagnetized region to come to a location where it is w before a frontedge of a second magnetized region. Further, the SVGMR element proceedsand a part of the SVGMR element comes to face the second magnetizedregion, where a magnetic field from the first magnetized region weakensso that the magnetization of the free magnetization layer of the SVGMRelement begins to rotate from a position it is anti-parallel to themagnetization of the pinned magnetization layer, and the SVGMR elementresistance decreases from the maximum value R1. When the SVGMR elementfurther proceeds from a location it faces the first magnetized regionand reaches a location it completely faces the second magnetized region,the magnetization of the free magnetization layer of the SVGMR elementbecomes parallel to the magnetization of the pinned magnetization layer,and the resistance becomes the minimum value R2, since a magnetic fieldfrom the first magnetized region comes not to work to the freemagnetization layer of the SVGMR element. A length of a region where theresistance of the SVGMR element changes from the minimum value R2 to themaximum value R1 or from the maximum value R1 to the minimum value R2 isalmost the same as the width w of the SVGMR element. The resistance ofthe SVGMR element changes in the same manner, even if it is the minimumvalue R2, when the SVGMR element is at a location the SVGMR elementfaces a first magnetized region, and is the maximum resistance R1, whenthe SVGMR element is at a location the SVGMR element faces a secondmagnetized region.

So, the SVGMR element resistance is the minimum value R2 at a locationthe SVGMR element faces a second/first magnetized region, and theresistance gradually rises from a location where it is w from an edge ofa first/second magnetized region, although the SVGMR element faces thesecond/first magnetized region, and becomes almost the maximum value R1at a location where the SVGMR element completely faces the first/secondmagnetized region. And when the SVGMR element resistance graduallydecreases from a location where it is w before an edge of thesecond/first magnetized region although the SVGMR element faces thefirst/second magnetized region, and becomes the minimum value R2 at alocation the SVGMR element completely faces the second/first magnetizedregion. Presuming that the first magnetized region has a longermagnetized region length λl and the second magnetized region has ashorter magnetized region length λs, a skirt length of a resistancemountain of an SVGMR element is w, and a peak length of the resistancemountain is almost λl−w or λs−w.

Whether the peak length of the resistance mountain of an SVGMR elementis λl−w or λs−w is determined by a magnetization of a pinnedmagnetization layer of the SVGMR element being in the same direction asa magnetization of a second magnetized region or a first magnetizedregion. However, since the first magnetized region and the secondmagnetized region can be replaced with each other, it should beunderstood that the peak length of the resistance mountain can be λl−wand λs−w. Here, since λl>λs is presumed, if a shorter magnetized regionlength λs is less than w, the SVGMR element cannot completely face theshorter magnetized region and the resistance cannot be a maximum/minimumvalue. So, it is necessary that a width w of an SVGMR element is equalto or shorter than the shorter magnetized region length λs.

In the magnetic encoder of the present invention, it is desirable that alonger magnetized region length λl is equal to or more than p+w, and ashorter magnetized region length λs is equal to or less than p−w.

When the longer magnetized region length λl is equal to or more than p+win the magnetic encoder, it leads to λl−p−w≧0. Incidentally, if aresistance mountain of an SVGMR element appears at a location facing thelonger magnetized region, an SVGMR element advancing or retreating pfrom the above-mentioned SVGMR element has a resistance mountain at alocation advancing or retreating p from the above-mentioned resistancemountain. Since a peak length of a resistance mountain of an SVGMRelement is almost λl−w, the two neighboring peaks of resistancemountains overlap each other with almost a length λl−p−w. The valuebeing zero or positive means that the two neighboring peaks overlap eachother. And when plural SVGMR elements are connected in series in eachsensor, a difference between a maximum value and a minimum value of thesummation of the resistances can be made larger.

By contrast, when a resistance mountain of an SVGMR element appears at alocation facing a shorter magnetic region, an SVGMR element advancing orretreating p from the above-mentioned SVGMR element has a resistancemountain at a location advancing or retreating p from a resistancemountain of the above-mentioned SVGMR element. A length from a skirt tothe other skirt of a resistance mountain of each SVGMR element is λs+w.Since a length λs of the shorter magnetized region is equal to or lessthan p−w, the length λs+w from a skirt to the other skirt of aresistance mountain of an SVGMR element is contained in a length p. Thismeans that skirts of two neighboring resistance mountains do not overlapeach other. So, when plural SVGMR elements in each sensor are connectedin series, a difference between a maximum value and a minimum value ofthe summation of the resistances can be made larger.

In the magnetic encoder of the present invention, it is preferable thatan SVGMR element of the second sensor is located between two neighboringSVGMR elements of the first sensor. Since both the first and the secondsensors are composed of the SVGMR elements of the equal number N, eachof which is apart by p from another, a distribution width of the SVGMRelements in each sensor is p·(the number N of SVGMR elements−1). Thedistribution width of all SVGMR elements contained in the first and thesecond sensors can be narrowed by positioning an SVGMR element of thesecond sensor between two neighboring SVGMR elements of the firstsensor.

According to the present invention, an electric signal having a cycle p,which is defined by 1/N of a cycle λl+λs of magnetic patterns of themagnetic medium, has been accomplished by a magnetic encoder havingSVGMR elements. Also, since SVGMR elements of large electric resistanceare used, a magnetic sensor of less electric power consumption has beenrealized. Furthermore, a large magneto-resistance variation ratio hasbeen obtained in a region of relatively small magnetic field, and amagnetic encoder capable of obtaining a stable output property (gapproperty) against a variation of a gap between a magnetic sensor and amagnetic medium has been realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective schematic view of a magnetic encoder using SVGMRelements according to the present invention;

FIG. 2 is a schematic view explaining an SVGMR element used in thepresent invention;

FIGS. 3A and 3B are graphs explaining a relationship between an electricresistance R and an external magnetic field H applied to an SVGMRelement, FIG. 3C is a graph explaining a relationship between anelectric resistance R and an external magnetic field H applied to acoupled GMR element, and FIG. 3D is a graph explaining a relationshipbetween an electric resistance R and an external magnetic field Happlied to an AMR element;

FIG. 4A is an explanatory view of a structure and a function of amagnetic encoder of EXAMPLE 2 of the present invention having a firstand a second sensors, each of which is composed of three SVGMR elements,and a magnetic medium, in which a first magnetized region is longer thana second magnetized region, FIG. 4B shows a graph explaining arelationship between an electric resistance of an SVGMR element in thefirst sensor and a location on the magnetic medium, FIG. 4C shows agraph explaining a relationship between an electric resistance ofanother SVGMR element in the first sensor and a location on the magneticmedium, FIG. 4D shows a graph explaining a relationship between anelectric resistance of a third SVGMR element in the first sensor and alocation on the magnetic medium, FIG. 4E shows a graph explaining arelationship between an electric resistance of the first sensor and alocation on the magnetic medium, FIG. 4F shows a graph explaining arelationship between an electric resistance of the second sensor and alocation on the magnetic medium, and FIG. 4G is a graph explainingrelationship between a midpoint electric potential output between thefirst and the second sensors and a location on the magnetic medium;

FIG. 5 is a view showing connections of the SVGMR elements in EXAMPLE 2by an equivalent circuit;

FIG. 6A is an explanatory view of a structure and a function of amagnetic encoder of EXAMPLE 3 of the present invention having a magneticmedium, in which a first magnetized region is shorter than a secondmagnetized region, FIG. 6B shows a graph explaining a relationshipbetween an electric resistance of an SVGMR element in a first sensor anda location on the magnetic medium, FIG. 6C shows a graph explaining arelationship between an electric resistance of another SVGMR element inthe first sensor and a location on the magnetic medium, FIG. 6D shows agraph explaining a relationship between an electric resistance of athird SVGMR element in the first sensor and a location on the magneticmedium, FIG. 6E shows a graph explaining a relationship between anelectric resistance of the first sensor and a location on the magneticmedium, FIG. 6F shows a graph explaining a relationship between anelectric resistance of a second sensor and a location on the magneticmedium, and FIG. 6G is a graph explaining relationship between amidpoint electric potential output between the first and the secondsensors and a location on the magnetic medium;

FIG. 7A is an explanatory view of a structure and a function of amagnetic encoder of EXAMPLE 4 according to the present invention havinga magnetic sensor, in which a first SVGMR element of a second sensor isdisposed between a first SVGMR element and a second SVGMR element of afirst sensor, FIG. 7B shows a graph explaining a relationship between anelectric resistance of an SVGMR element in the first sensor and alocation on a magnetic medium, FIG. 7C shows a graph explaining arelationship between an electric resistance of another SVGMR element inthe first sensor and a location on the magnetic medium, FIG. 7D shows agraph explaining a relationship between an electric resistance of athird SVGMR element in the first sensor and a location on a magneticmedium, FIG. 7E shows a graph explaining a relationship between anelectric resistance of the first sensor and a location on the magneticmedium, FIG. 7F shows a graph explaining a relationship between anelectric resistance of the second sensor and a location on the magneticmedium, and FIG. 7G is a graph explaining relationship between amidpoint electric potential output between the first and the secondsensors and a location on the magnetic medium;

FIG. 8A is an explanatory view of a structure and a function of amagnetic encoder of EXAMPLE 5 according to the present invention havinga magnetic sensor, in which each of a first and a second sensors of themagnetic sensor is composed of four SVGMR elements, and in which a firstmagnetized region is shorter than a second magnetized region, FIG. 8Bshows a graph explaining a relationship between an electric resistanceof an SVGMR element in the first sensor and a location on a magneticmedium, FIG. 8C shows a graph explaining a relationship between anelectric resistance of another SVGMR element in the first sensor and alocation on the magnetic medium, FIG. 8D shows a graph explaining arelationship between an electric resistance of a third SVGMR element inthe first sensor and a location on the magnetic medium, FIG. 8E shows agraph explaining a relationship between an electric resistance of aforth SVGMR element in the first sensor and a location on the magneticmedium, FIG. 8F shows a graph explaining a relationship between anelectric resistance of the first sensor and a location on the magneticmedium, FIG. 8G shows a graph explaining a relationship between anelectric resistance of the second sensor and a location on the magneticmedium, and FIG. 8H is a graph explaining relationship between amidpoint electric potential output between the first and the secondsensors and a location on the magnetic medium;

FIG. 9 is a view showing connections of the SVGMR elements in EXAMPLE 5by an equivalent circuit; and

FIG. 10 is a graph showing a relationship (gap property) between amagnetic sensor output and a gap length in magnetic encoders accordingto the present invention having SVGMR elements and in a comparativemagnetic encoder having coupled GMR elements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, magnetic encoders of EXAMPLES according tothe present invention will be described in details below. Forconvenience of understanding, the same numeral references will be usedfor the same parts and the same places. EXAMPLES will he explained,using a spin-valve type magneto-resistance effect film for SVGMRelements, in which a magnetization of a free magnetization layer isopposite to a magnetization of a pinned magnetization layer, and anelectric resistance is high, when an external magnetic field is notapplied, and the electric resistance of the SVGMR element reduces whenan external magnetic field is applied to the SVGVR element in the samedirection as the magnetization of the pinned magnetization layer of theSVGMR element, while the electric resistance of the SVGMR element doesnot change when an opposite external magnetic field is applied to theSVGMR element. When the magnetization of the free magnetization layer isin the same direction as the magnetization of the pinned magnetizationlayer, the electric resistance of the SVGMR element is minimum, while,when the magnetization of the free magnetization layer is opposite, amagneto-resistance change does not appear, and the electric resistanceof the SVGMR element is maximum.

EXAMPLE 1

FIG. 1 shows a perspective schematic view for explaining a magneticencoder having SVGMR elements. The magnetic encoder 1 is composed of amagnetic medium 2 and a magnetic sensor 6. On the magnetic medium 2, twomagnetized regions, that is, first magnetized regions 21 and secondmagnetized regions 22, which are magnetized oppositely to each other,are arranged successively and alternately along the medium extending. Inthe following explanation, it is presumed that the length λl of thefirst magnetized regions 21 is longer than the length λs of the secondmagnetized regions 22. In the magnetic sensor 6, six SVGMR elements 5are formed in rectangular flat surfaces extending perpendicularly to themagnetic medium 2 extending on a base material 4, and ends of the SVGMRelements 5 are connected through lead wires (not shown) to a flexibleprint circuit 3. Among the six SVGMR elements, three SVGMR elementselectrically connected in series constitute a first sensor 51, and theother three SVGMR elements electrically connected in series constitute asecond sensor 52. The magnetic medium 2 faces the SVGMR elements 5having the rectangular flat surfaces with a predetermined gap. When themagnetic sensor moves relatively to the magnetic medium, a magneticfield being applied to the SVGMR elements varies and the resistances ofthe SVGMR elements change. In the following explanation, it is presumedthat the magnetic medium is fixed and the magnetic sensor moves.

In FIG. 2, the SVGMR element 5 is shown in a schematic view. In amanufacture of the SVGMR element 5, after laminating a pinnedmagnetization layer 10, a non-magnetic conductive layer 11 and a freemagnetization layer 12 in the order on a base material 4, a resist-maskwas made by a photolithograph, and a rectangular element was formed byion milling. As the base material 4, aluminosilicate glass of thermalexpansion coefficient α of 38×10⁻⁷ deg.⁻¹ was used. The pinnedmagnetization layer 10 had a composition of Co₉₀Fe₁₀ (atomic %) and 5 nmin thickness on an anti-ferromagnetic layer of Mn₅₀Pt₅₀ (atomic %) andof 12 nm in thickness. The non-magnetic conductive layer 11 was copperand 3 nm in thickness. The free magnetization layer 12 was a two-layerfilm of Ni₈₅Fe₁₅ layer and Co₉₀Fe₁₀ layer and 5 nm in total thickness.The thickness ratio of Ni₈₅Fe₁₅ layer to Co₉₀Fe₁₀ layer was 3:1 to 5:1.The pinned magnetization layer 10 was sputtered im a magnetic field ofabout 240 A/m (about 30 Oe) to fix the magnetization. The NiFe layer inthe free magnetization layer was sputtered in a magnetic field to makeit magnetic anisotropy and to enhance the magnetic property.

After a resist-mask was formed by photolithograph technology on aspin-valve type giant magneto-resistance effect film made on the basematerial 4, SVGMR elements 5 were formed in an aimed shape by ionmilling with argon ion. The SVGMR elements had almost rectangularshapes. In FIG. 2, the width of the rectangular SVGMR element is shownby w and the length is by L. The length L was made longer than the widthof the magnetic medium, and the SVGMR elements were connectedelectrically in series outside of the magnetic medium width. Byzigzagging the spin-valve type giant magneto-resistance effect film, theelements were connected. Since an external magnetic field is not appliedto the connections of the elements, they do not show magneto-resistancevariation.

A magnetization direction of the pinned magnetization layer 10 is shownby a solid arrow 13, while external magnetic field directions applied tothe free magnetization layer 12 are shown by a dot-chain arrow 14 and adotted arrow 15. Since the external magnetic field applied in thedot-chain arrow 14 is in the same direction as the magnetization of thepinned magnetization layer, an electric resistance of the SVGMR element5 reduces according to the external magnetic field increasing. When theexternal magnetic field is applied in the dotted arrow 15, the magneticfield is opposite to the magnetization of the pinned magnetizationlayer, and the electric resistance of the SVGMR element 5 does notchange. FIG. 3 shows relationships between electric resistances R and anexternal magnetic field H. FIG. 3A is a resistance change when anexternal magnetic field is applied to an SVGMR element. The electricresistance of the SVGMR element is R1 when no magnetic field is applied,and the electric resistance reduces and is saturated at R2 when amagnetic field is applied in a plus direction, that is, in the samedirection as the magnetization of the pinned magnetization layer. Evenwhen a magnetic field applied in a minus direction, that is, in adirection opposite to the magnetization of the pinned magnetizationlayer, a magneto-resistance variation does not occur, and an electricresistance is maintained at R1. A value obtained by a formula(R1−R2)/R1×100 (%) is called a magneto-resistance variation ratio. FIG.3B shows a relationship between a change of an electric resistance andan external magnetic field, using an SVGMR element, in which an electricresistance on an element does not change when the magnetic field isapplied in the same direction as a magnetization of a pinnedmagnetization layer, and changes when the magnetic field is appliedopposite to the magnetization of the pinned magnetization layer. Theelectric resistance of the SVGMR element is minimum when a magnetizationof a free magnetization layer is in the same direction as themagnetization of the pinned magnetization layer, and when it isopposite, a magneto-resistance variation does not occur, and theelectric resistance of the SVGMR element is maximum. For comparison,relationships between electric resistances and external magnetic fieldsof a coupled GMR (giant magneto-resistance effect) element and of an AMR(anisotropic magneto-resistance effect) element are shown in FIG. 3C andFIG. 3D, respectively. In the coupled GMR element and the AMR element,magneto-resistance variation occurs in both directions of an externalmagnetic field increasing and decreasing unlike the SVGMR element. Sincethe magneto-resistance variation occurs in both directions of theexternal magnetic field increasing and decreasing in such a way, anelectric signal obtained has the same cycle as a unit magnetized regionlength λ, that is, a magnetization length of the magnetic medium. Aninitial electric resistance R3 (without an applied magnetic field) of acoupled GMR element is about 322Ω, while an initial electric resistanceR1 of an SVGMR element is about 1560Ω that is about five times theinitial electric resistance of the coupled GMR element. The electricresistances R3 and R1 are examples of elements of 5 μm in element widthw and 1000 μm in element length L. The difference in the initialelectric resistances becomes a difference in electric power consumptionsin magnetic sensors. The more the initial electric resistance, the lessthe electric power consumption in a magnetic sensor.

EXAMPLE 2

Referring to FIG. 4, in which a first magnetized region length λl islonger than a second magnetized region length λs on a magnetic medium 2,a work of a magnetic encoder will be described. FIG. 4A explains alocation relationship between SVGMR elements 51 a to 52 c of a magneticsensor 6 and the magnetic medium 2, and FIGS. 4B to 4G show graphs ofelectric resistances and an electric signal with respect to a locationon the magnetic medium 2 where the SVGMR elements 51 a to 52 c are.Electric resistance graphs of an SVGMR element 51 a of a first sensor51, another SVGMR element 51 b of the first sensor 51, a third SVGMRelement 51 c of the first sensor 51, the first sensor 51 composed of theSVGMR elements 51 a to 51 c, a second sensor 52 composed of SVGMRelements 52 a to 52 c are shown in FIGS. 4B, 4C, 4D, 4E and 4F,respectively. In the magnetic sensor 6, the six SVGMR elements 51 a to52 c are disposed on a base material. Each of the SVGMR elements has anelement width w, and an SVGMR element is at a distance p, determined by(λl+λs)/3, from another in each of the sensors. The second sensor 52 isshifted by p/2 after the first sensor 51. Arrow attached to each of theSVGMR elements means a magnetization of a pinned magnetization layer inFIG. 4A. In the magnetic medium 2, the first magnetized region 21 ismagnetized oppositely to the second magnetized region 22 and longer thanthe second magnetized region 22. The length of the first magnetizedregion is denoted as λl, and the length of the second magnetized regionis denoted as λs. A direction of a leakage magnetic field caused by eachmagnetic region is shown by a dotted arrow connecting both ends of eachof the first and the second magnetic regions 21, 22 of the magneticmedium.

FIG. 5 shows connections of the SVGMR elements 51 a to 52 c in anequivalent circuit. The SVGMR elements 51 a to 51 c in the firstmagnetic sensor 51 are connected in series, and in the same manner, theSVGMR elements 52 a to 52 c in the second magnetic sensor 52 areconnected in series. A terminal of the SVGMR element 51 c of the firstmagnetic sensor is connected to a terminal of SVGMR element 52 a of thesecond magnetic sensor, and the connected terminal is connected to anoutput terminal to take out a midpoint electric potential Vout. Theother terminal of the SVGMR element 51 a of the first magnetic sensor 51is connected to an electric source Vcc, and the other terminal of theSVGMR element 52 c of the second sensor 52 is down to the ground.

When the magnetic sensor 6 moves in the direction of the arrow in FIG.4A, the SVGMR elements 51 a to 51 c receive a leakage magnetic fieldfrom the magnetic medium, the SVGMR element 51 a changes in an electricresistance as shown in FIG. 4B, the SVGMR element 51 b changes in anelectric resistance as shown in FIG. 4C and the SVGMR element 51 cchanges in an electric resistance as shown in FIG. 4D. The maximum valueof the electric resistance is set to R1, and the minimum value of theelectric resistance is set to R2. FIG. 4E shows a composite electricresistance, which is equivalent to an electric resistance of the firstsensor 51, of the SVGMR elements 51 a to 51 c. Although an electricresistance cycle of each of the SVGMR; element 51 a in FIG. 4B, theSVGMR element 51 b in FIG. 4C and the SVGMR element 51 c in FIG. 4D isλl+λs, the composite electric resistance (see FIG. 4E) of the SVGMRelements 51 a to 51 c has a maximum resistance variation of R1−R2 and acycle (λl+λs)/3, since the elements are disposed at a distance (λl+λs)/3from each other. A composite electric resistance of a second sensor 52is shown in FIG. 4F in the same manner. In FIG. 4F that advances inphase by p/2 from FIG. 4E, a midpoint electric potential Vout that is anoutput of the magnetic sensor 6 is an electric signal having a centervoltage Vcc/2 of an amplitude and a cycle (λl+λs)/3. Since the outputamplitude becomes larger with a larger difference between R1 and R2, anoutput can be larger when an element with a larger resistance variationlike an SVGMR element is used. Using a configuration of SVGMR elementsas in the present invention, in which an SVGMR element distance in eachof the first and the second sensors is p that is a third of the sum ofthe first magnetized region length λl plus the second magnetized regionlength λs, and in which a distance between the first and the secondsensors is p/2 that is a half of the SVGMR element distance, a magneticencoder of the high resolution has been accomplished, which has not beenobtained only by a substitution of SVGMR elements for conventionalelements.

As apparent from FIG. 4B, a resistance change region is almost the sameas an SVGMR element width w. In the drawing, a range where the SVGMRelement resistance is more than R2 has a length λs+w that is a sum ofthe second magnetized region length λs plus the SVGMR element width w.When the SVGMR element width w increases, the resistance mountain widthis broadened, and a skirt of a resistance mountain of an SVGMR elementof a sensor overlaps a skirt of a resistance mountain of another SVGMRelement of the sensor. When skirts of resistance mountains overlap eachother, the minimum value of resistance becomes larger than R2. Becauseof that, resistance variation in each SVGMR element becomes smaller thana resistance variation of the case of no skirt overlapping, to reduce anamplitude of the output Vout shown in FIG. 4G.

The overlap of skirts of resistance mountains is necessarily caused whenthe first and the second magnetized regions have the same length. So, itis necessary that the first magnetized region differs in length from thesecond magnetized region. In this EXAMPLE, three resistance mountainwidths 3(λs+w) of the three SVGMR elements are contained in a totallength λl+λs of the first magnetized region length λl and the secondmagnetized region length λs. When the first magnetized region is longerthan the second magnetized region, the overlapping of the skirts of theresistance mountains of the SVGMR elements reduces, and further whenλl+λs (=3p)≧3(λs+w), the skirts of the resistance mountains of the SVGMRelements do not overlap each other.

EXAMPLE 3

Referring to FIGS. 6A to 6G, a magnetic encoder of EXAMPLE 3 will bedescribed, which is similar to the magnetic encoder of EXAMPLE 2 shownin FIG. 4A with an exception that a magnetic medium 2 has a first regionshorter than a second magnetized region. FIG. 6A explains a locationrelationship between SVGMR elements 51 a to 52 c of a magnetic sensor 6and the magnetic medium 2, and FIGS. 6B to 6G show graphs of electricresistances and an electric signal with respect to a location on themagnetic medium 2 where the SVGMR elements 51 a to 52 c are. Electricresistance graphs of an SVGMR element 51 a of a first sensor 51, anotherSVGMR element 51 b of the first sensor 51, a third SVGMR element 51 c ofthe first sensor 51, the first sensor 51 composed of the SVGMR elements51 a to 51 c, a second sensor 62 composed of SVGMR elements 52 a to 52 care shown in FIGS. 6B, 6C, 6D, 6E and 6F, respectively. In the magneticsensor 6, the six SVGMR elements 51 a to 52 c are disposed on a basematerial. Each of the SVGMR elements in each sensor has an element widthw, and an SVGMR element is at a distance p, determined by (λl+λs)/3,from another in each of the first and the second sensors. The secondsensor 52 is shifted by p/2 after the first sensor 51. Arrow attached toeach of the SVGMR elements means a magnetization of a pinnedmagnetization layer in FIG. 6A. In the magnetic medium 2, the firstmagnetized region 21 is magnetized oppositely to the second magnetizedregion 22, and the first magnetized region 21 is shorter than the secondmagnetized region 22. The length of the first magnetized region is setto λs, and the length of the second magnetized region is set to λl. Adirection of a leakage magnetic field caused by each magnetic region isshown by a dotted arrow connecting both ends of each of the first andthe second magnetic regions 21, 22 of the magnetic medium 2.

When the magnetic sensor 6 moves in the direction of the arrow in FIG.6A, the SVGMR elements 51 a to 51 c receive a leakage magnetic fieldfrom the magnetic medium, the SVGMR element 51 a changes in an electricresistance as shown in FIG. 6B, the SVGMR element 51 b changes in anelectric resistance as shown in FIG. 6C, and the SVGMR element 51 cchanges in an electric resistance as shown in FIG. 6D. The maximum valueof the electric resistance is set to R1, and the minimum value of theelectric resistance is set to R2. FIG. 6E shows a composite electricresistance, which is equivalent to an electric resistance of the firstsensor 51, of the SVGMR elements 51 a to 51 c. Although an electricresistance cycle of each of the SVGMR element 51 a in FIG. 6B, the SVGMRelement 51 b in FIG. 6C and the SVGMR element 51 c in FIG. 6D is λl+λs,the composite electric resistance (see FIG. 6E) of the SVGMR elements 51a to 51 c has a maximum resistance variation of R1−R2 and a cycle(λl+λs)/3, since the elements are disposed at a distance p from eachother. A composite electric resistance of a second sensor 52 is shown inFIG. 6F in the same manner. In FIG. 6F that advances in phase by p/2from FIG. 6E, a midpoint electric potential Vout that is an output ofthe magnetic sensor 6 is an electric signal having a center voltageVcc/2 of an amplitude and a cycle (λl+λs)/3 as shown in FIG. 6G. Using aconfiguration of SVGMR elements explained above, a magnetic encoder ofthe high resolution has been accomplished, which has not been obtainedonly by a substitution of SVGMR elements for conventional elements.

EXAMPLE 4

A magnetic encoder comprising a magnetic medium 2, in which a firstmagnetized region 21 is longer than a second magnetized region 22, and amagnetic sensor 6 having a structure, in which a first SVGMR element 52a of a second sensor is positioned between a first SVGMR element 51 aand a second SVGMR element 51 b of a first sensor, will be described asEXAMPLE 4, referring to FIG. 7. The first magnetized region length isset to λl, and the second magnetized region length is set to λs. Asshown in FIG. 7A, an SVGMR element distance in each of the first and thesecond sensors is p that is determined by (λl+λs)/3, and the first SVGMRelement 52 a of the second sensor is shifted by p/2 from the first SVGMRelement 51 a of the first sensor. The second SVGMR element 51 b of thefirst sensor is apart p/2 from the first SVGMR element 52 a of thesecond sensor. And, each SVGMR element width is w. When the magneticsensor 6 moves in an arrow direction, the SVGMR elements 51 a to 51 creceive a leakage magnetic field from the magnetic medium, and electricresistances in the SVGMR elements 51 a, 51 b and 51 c change as shown inFIG. 7B, FIG. 7C and FIG. 7D, respectively. The maximum value of theelectric resistance is set to R1, and the minimum value of the electricresistance is set to R2. A composite electric resistance of the SVGMRelements 51 a to 51 c, which is equivalent to an electric resistance ofthe first sensor, is shown in FIG. 7E. Although each electric resistanceof the SVGMR elements 51 a, 51 b and 51 c shown in FIG. 7B, FIG. 7C andFIG. 7D has a cycle λl+λs, the composite electric resistance of theSVGMR elements 51 a to 51 c has a maximum resistance variation of R1−R2and a cycle (λl+λs)/3 (see FIG. 7E), since the elements are disposed ata distance p from each other. A composite electric resistance of thesecond sensor is shown in FIG. 7F in the same manner. In FIG. 7Fadvancing in phase by p/2 from FIG. 7E, a midpoint electric potentialVout that is an output of the magnetic sensor 6 is an electric signalhaving a center voltage Vcc/2 of an amplitude and a cycle (λl+λs)/3, asshown in FIG. 7G.

Since the first magnetized region length is longer than the secondmagnetized region length in this EXAMPLE 4 as in EXAMPLE 2, the electricresistances and the midpoint electric potential of the SVGMR elements 51a to 52 c change in the same manner as in EXAMPLE 2, and the magneticencoder of the high resolution has been obtained. In FIG. 7A, an elementdistribution length from a top SVGMR element 51 a to an element 52 c atthe tail end is {2p+(p/2)+w}. By contrast, the SVGMR elementdistribution length was {2p+(p/2)+2p+w} in the magnetic sensor, in whichthe second sensor was disposed after the first sensor, shown in EXAMPLE2. The magnetic sensor width can be made smaller by the configuration ofEXAMPLE 4 and cheaper, since more magnetic sensors can be produced froma wafer. Also, miniaturization has been realized.

EXAMPLE 5

A magnetic encoder comprising a magnetic medium 2, in which a firstmagnetized region is shorter than a second magnetized regions, and amagnetic sensor 6, in which each of a first sensor 51 and a secondsensor 52 has four SVGMR elements, will be described as EXAMPLE 5,referring to FIG. 8. The first sensor 51 is composed of the SVGMRelements 51 a to 51 d, and the second sensor 52 is composed of the SVGMRelements 52 a to 52 d. Each SVGMR element distance in the first and thesecond sensors is set to p that is determined by (λl+λs)/4 from thefirst magnetized region length λs and the second magnetized regionlength λl, and the first SVGMR element 52 a of the second sensor isdisposed apart by p/2 from the fourth SVGMR element 51 d of the firstsensor.

FIG. 9 shows connections of the SVGMR elements 51 a to 52 d in anequivalent circuit. The SVGMR elements 51 a to 51 d in the first sensor51 are connected in series, and in the same manner, the SVGMR elements52 a to 52 d in the second sensor 52 are connected in series. A terminalof the SVGMR element 51 d of the first sensor 51 is connected to aterminal of SVGMR element 52 a of the second sensor 52, and theconnected terminal is connected to an output terminal to take out amidpoint electric potential. The other terminal of the SVGMR element 51a of the first sensor 51 is connected to an electric source Vcc, and theother terminal of the SVGMR element 52 d of the second sensor 52 is downto the ground.

When the magnetic sensor 6 moves in an arrow direction in FIG. 8A, theSVGMR elements 51 a to 51 d of the first sensor receive a leakagemagnetic field from the magnetic medium 2, the first SVGMR element 51 achanges in electric resistance as shown in FIG. 8B, and the second SVGMRelement 51 b changes in electric resistance as shown in FIG. 8C, thethird SVGMR element 51 c changes in electric resistance as shown in FIG.8D, and the forth SVGMR element 51 d changes in electric resistance asshown in FIG. 8E. The maximum value of the electric resistance is set toR1, and the minimum value of the electric resistance is set to R2. FIG.8F shows a composite electric resistance of the SVGMR elements 51 a to51 d, which is equivalent to an electric resistance of the first sensor.And, FIG. 8G shows a composite electric resistance of the SVGMR elements52 a to 52 d, which is equivalent to an electric resistance of thesecond sensor. Although an electric resistance cycle of each of theSVGMR elements 51 a to 5 d in FIGS. 8B to 8E is λl+λs, the compositeelectric resistance of the SVGMR elements 51 a to 51 d has a maximumresistance variation of R1−R2 and a cycle (λl+λs)/4, since they aredisposed with an element distance (λl+λs)/4. In the same manner, acomposite electric resistance of the second sensor has a cycle (λl+λs)/4as shown in FIG. 8G and is p/2 in phase difference from the compositeelectric resistance shown in FIG. 8F. A midpoint electric potential Voutthat is an output of the magnetic sensor 6 is an electric signal havinga cycle (λl+λs)/4 as shown in FIG. 8H.

EXAMPLE 6

In FIG. 10, a gap property of the magnetic encoder according to thepresent invention is shown. By changing a gap between a magnetic mediumand a magnetic sensor with an interval of 5 μm from 0 μm to 25 μm, arelationship of a magnetic sensor output with respect to a gap length,that is, a gap property, was measured. In the magnetic sensors used herethat were like those used in EXAMPLES 2 and 3, the second sensor wasshifted by p/2 after the first sensor. Distances p between SVGMRelements in each sensor were 20 μm, and width w of the SVGMR element was5 μm. A magnetic medium, in which the sum λl+λs of the first magnetizedregion length plus the second magnetized region length was 60 μm, wasused for a magnetic encoder having three SVGMR elements for each of thefirst and the second sensors. And, a magnetic medium, in which the sumλl+λs of the first magnetized region length plus the second magnetizedregion length was 80 μm, was used for the magnetic encoder having fourSVGMR elements for each of the first and the second sensors. Themagnetic properties of a magnetic material used in the magnetic mediumwere coercive force He: 217 kA/m, residual magnetic flux density Br: 1.4T and squareness R: 0.8. The measurements were carried out in Condition1: the magnetic encoder having three SVGMR elements for each of thefirst and the second sensors was used, a first magnetized region waslonger than a second magnetized region, and a length difference betweenthem was w, Condition 2: the magnetic encoder having three SVGMRelements for each of the first and the second sensors was used, a firstmagnetized region was shorter than a second magnetized region, and alength difference between them was w, and Condition 3: the magneticencoder having four SVGMR elements for each of the first and the secondsensors was used, a first magnetized region was shorter than a secondmagnetized region, and a length difference between them was w. Forcomparison, a gap property about coupled GMR sensors was measured. Inthe coupled GMR sensors, a first magnetized region length was equal to asecond magnetized region length, their lengths were 40 μm, and two GMRelements were disposed at a distance of 20 μm from each other.

The gap property was evaluated with a gap length range providing anoutput more than 80% of the maximum output. A vertical axis of FIG. 10shows a ratio of an output to the maximum output set to 1 in eachCondition. As apparent from FIG. 10, gap length ranges for sensors usingSVGMR elements in all the Conditions are broader in comparison with thecoupled GMR sensors. In the coupled GMR sensors, the magnetic sensoroutput sharply decreased when the gap became longer, and the gap lengthrange providing output more than 80% was as small as 0 μm to 1.8 μm. Inthe sensors of SVGMR elements, the gap length range of Condition 1 was 0μm to 11 μm, and the gap length range of about six times that of thecoupled GMR sensors was obtained. The gap length ranges of Conditions 2and 3 were 0 μm to 15.5 μm, which were about 8.6 times that of thecoupled GMR sensors. The fact that a larger gap length range wasobtained like this supports that the SVGMR elements work in a smallmagnetic field.

1. A magnetic encoder comprising: a magnetic medium extending in adirection and having first magnetized regions and second magnetizedregions, which are disposed successively and alternately with each otheron the medium and magnetized oppositely to one another along the mediumextending, and a magnetic sensor movable relatively to the medium alongthe medium extending, wherein the first and the second magnetizedregions are different in length from one another, of which a length oflonger ones is denoted as λl, and a length of shorter ones is denoted asλs, wherein the magnetic sensor is composed of a first sensor and asecond sensor, each of which is composed of SVGMR elements of the equalnumber N of three or more, which have a rectangular surface extendingperpendicularly to the medium extending and facing the medium with apredetermined gap and are electrically connected in series, wherein eachof the SVGMR elements in each of the first and the second sensors isapart by p defined by (λl+λs)/N from another SVGMR element along themedium extending, wherein one of the SVGMR elements in the first sensoris at a distance of p(½+n) from one of the SVGMR elements in the secondsensor along the medium extending, wherein n is 0 or a positive integer,wherein each of the SVGMR elements is a lamination of a pinnedmagnetization layer, a non-magnetic conductive layer and a freemagnetization layer in their order, the pinned magnetization layers inall of the SVGMR elements have magnetizations in the same directionalong the medium extending, and the SVGMR elements show a minimumelectric resistance, when an external magnetic field is applied to theSVGMR elements in the same direction as the magnetizations of the pinnedmagnetization layers of the SVGMR elements, and a maximum electricresistance, when an external magnetic field is applied to the SVGMRelements in the direction opposite to the magnetizations of the pinnedmagnetization layers of the SVGMR elements, and wherein an electricterminal of the first sensor is electrically connected to an electricterminal of the second sensor, and a signal output is taken out from theconnected electric terminals between the first sensor and the secondsensor, during a measurement voltage is applied between the otherelectric terminal of the first sensor and the other electric terminal ofthe second sensor.
 2. A magnetic encoder as set forth in claim 1,wherein a width w of each of the SVGMR elements along the mediumextending is equal to or less than λs.
 3. A magnetic encoder as setforth in claim 2, wherein λl is equal to or more than p+w, and λs isequal to or less than p−w.
 4. A magnetic encoder as set forth in claim3, wherein a SVGMR element of the second sensor is located between twoneighboring SVGMR elements of the first sensor.